organic matter and minerals after death and decomposition of microalgae biomass
(Saadatnia and Riahi 2009); (5) reduction in soil salinity (Al-sherif et al. 2015);
(6) prevention of weed growth and production of antiviral and antibacterial substances to protect plants (Abd El Baky and El-Baroty 2013; Dahms et al. 2006;
Hannon et al. 2010); and (7) increase in soil phosphate by excretion of organic acids
(Singh et al. 2016). Some nitrogen-fixing species, such as Anabaena and Nostoc,
can be directly used as fertilizers for agricultural purposes (Hamed 2016) through
direct inoculation in soils, or green algae can be applied as dry powder with high
percentage of macronutrients, considerable amounts of micronutrients, and amino
acids (Faheed and Abd-El Fattah 2008; Garcia-Gonzalez and Sommerfeld 2016).
Biomaterials: Biomaterials use complex structures of biomass for application in
plastics, coatings and surface treatment materials, packaging materials, fibers and
textiles, elastomers, lubricants and fillers, surfactants, and functional materials
(Budzianowski 2017). Biomaterials have a bright future in replacing materials from
fossil resources. The biochemical composition of biomass defines the potential
biomaterial that can be produced. Proteins are the main platform molecules to make
thermoplastics, foams, adhesives, biocomposites, and flocculants, and bioplastics
are made from starch (Laurens et al. 2017a). In the case of microalgae biomass,
bioplastics can be derived from any of the three major component fractions (lipids,
proteins, and carbohydrates) (IEA 2017). Some researchers have described the use
of the whole algae as filler material for different types of plastics, such as
polypropylene (Zhang et al. 2000a), polyvinyl chloride (Zhang et al. 2000b,
polyethylene (Otsuki and Zhang 2004; Zeller et al. 2013), blends of algae and
starch (Kipngetich and Hillary 2013), or proteins (Reddy et al. 2013; Shi et al.
2011). But microalgae can also produce high-quality biodegradable plastics, such as
polyhydroxyalkanoates (PHA) (Balaji et al. 2013; Chaogang et al. 2010; Haase
et al. 2011; Rahman and Miller 2017). Surfactants can also be produced from
microalgal sterols and phytol and have a high market potential of around 8,436
billion dollars for a five-year period (IEA 2017; Laurens et al. 2017a). Furthermore,
asphalts can be made from microalgae biomass as well (Chailleux et al. 2012).
Bioenergies: A wide range of biofuels for bioenergy can be produced from
microalgae biomass and all petroleum fuels, such as hydrocarbons, asphalts, liquid
(kerosene, gasoline, diesel), and gaseous fuels (methane, syngas); even more, the
biocrude can be made from microalgae biomass (Bahadar and Bilal Khan 2013;
Budzianowski 2017; Chew et al. 2017). Biofuels are the third sector in terms of
patent applications due to decades of research. However, given the noneconomic
viability, this area has experienced a slow growth although it has aroused a lot of
interest (Chilton et al. 2016). Hydrogen can be produced directly by microalgae
photolysis. Other biofuels, such as ethanol and biogas, can be obtained from
transformation of carbohydrates (starch, sugars, or other polymers) by fermentation
into bioethanol (Chng et al. 2015) and/or anaerobic digestion, respectively.
Bioelectricity can be also generated by integration of microalgae into a microbial
fuel cell using microalgae in the cathode compartment and bacteria in the anode
(Gouveia et al. 2014; Lee et al. 2015). This integration becomes especially favorable when considering that phototrophic organisms act as in situ generators of
5 Microalgae Biorefineries for Energy …
97
(Saadatnia and Riahi 2009); (5) reduction in soil salinity (Al-sherif et al. 2015);
(6) prevention of weed growth and production of antiviral and antibacterial substances to protect plants (Abd El Baky and El-Baroty 2013; Dahms et al. 2006;
Hannon et al. 2010); and (7) increase in soil phosphate by excretion of organic acids
(Singh et al. 2016). Some nitrogen-fixing species, such as Anabaena and Nostoc,
can be directly used as fertilizers for agricultural purposes (Hamed 2016) through
direct inoculation in soils, or green algae can be applied as dry powder with high
percentage of macronutrients, considerable amounts of micronutrients, and amino
acids (Faheed and Abd-El Fattah 2008; Garcia-Gonzalez and Sommerfeld 2016).
Biomaterials: Biomaterials use complex structures of biomass for application in
plastics, coatings and surface treatment materials, packaging materials, fibers and
textiles, elastomers, lubricants and fillers, surfactants, and functional materials
(Budzianowski 2017). Biomaterials have a bright future in replacing materials from
fossil resources. The biochemical composition of biomass defines the potential
biomaterial that can be produced. Proteins are the main platform molecules to make
thermoplastics, foams, adhesives, biocomposites, and flocculants, and bioplastics
are made from starch (Laurens et al. 2017a). In the case of microalgae biomass,
bioplastics can be derived from any of the three major component fractions (lipids,
proteins, and carbohydrates) (IEA 2017). Some researchers have described the use
of the whole algae as filler material for different types of plastics, such as
polypropylene (Zhang et al. 2000a), polyvinyl chloride (Zhang et al. 2000b,
polyethylene (Otsuki and Zhang 2004; Zeller et al. 2013), blends of algae and
starch (Kipngetich and Hillary 2013), or proteins (Reddy et al. 2013; Shi et al.
2011). But microalgae can also produce high-quality biodegradable plastics, such as
polyhydroxyalkanoates (PHA) (Balaji et al. 2013; Chaogang et al. 2010; Haase
et al. 2011; Rahman and Miller 2017). Surfactants can also be produced from
microalgal sterols and phytol and have a high market potential of around 8,436
billion dollars for a five-year period (IEA 2017; Laurens et al. 2017a). Furthermore,
asphalts can be made from microalgae biomass as well (Chailleux et al. 2012).
Bioenergies: A wide range of biofuels for bioenergy can be produced from
microalgae biomass and all petroleum fuels, such as hydrocarbons, asphalts, liquid
(kerosene, gasoline, diesel), and gaseous fuels (methane, syngas); even more, the
biocrude can be made from microalgae biomass (Bahadar and Bilal Khan 2013;
Budzianowski 2017; Chew et al. 2017). Biofuels are the third sector in terms of
patent applications due to decades of research. However, given the noneconomic
viability, this area has experienced a slow growth although it has aroused a lot of
interest (Chilton et al. 2016). Hydrogen can be produced directly by microalgae
photolysis. Other biofuels, such as ethanol and biogas, can be obtained from
transformation of carbohydrates (starch, sugars, or other polymers) by fermentation
into bioethanol (Chng et al. 2015) and/or anaerobic digestion, respectively.
Bioelectricity can be also generated by integration of microalgae into a microbial
fuel cell using microalgae in the cathode compartment and bacteria in the anode
(Gouveia et al. 2014; Lee et al. 2015). This integration becomes especially favorable when considering that phototrophic organisms act as in situ generators of
5 Microalgae Biorefineries for Energy …
97